With reference to FIG. 1, there is illustrated a schematic representation of one form of an aircraft engine 50 used as a power plant for an aircraft 52. In one form the aircraft engine 50 can be a gas turbine engine having a variety of forms including turbo jet, turbo fan, and turbo shaft, to set forth just a few non-limiting examples. The aircraft 52 includes a lift fan 54 capable of producing a vertical lift force useful for providing hovering or short takeoff and vertical landing operations, among other uses. As used herein, the term “aircraft” includes, but is not limited to, helicopters, airplanes, unmanned space vehicles, fixed wing vehicles, variable wing vehicles, rotary wing vehicles, unmanned combat aerial vehicles, tailless aircraft, hover crafts, and other airborne and/or extraterrestrial (spacecraft) vehicles. Further, the present inventions are contemplated for utilization in other applications that may not be coupled with an aircraft such as, for example, industrial applications, power generation, pumping sets, naval propulsion and other applications known to one of ordinary skill in the art.
A clutch 56 is depicted in FIG. 1 and is used to selectively couple the aircraft engine 50 to lift fan 54. In the illustrative form the clutch 56 is depicted as coupling an input shaft 58 from the aircraft engine 50 to an output shaft 60 of the lift fan 54. In some embodiments the input shaft 58 can be directly coupled to a spool shaft (not depicted) of the aircraft engine 50, but in other embodiments the input shaft 58 can be coupled through any combination of lay shafts, clutches, and/or gearboxes, to set forth just a few non-limiting examples. Furthermore, the output shaft 60 can be coupled to a fan rotor and/or shaft (not shown) of the lift fan 54 through any combination of lay shafts, clutches, and/or gearboxes, to set forth just a few non-limiting examples. The clutch 56 of the illustrative embodiment is a multi-plate clutch having friction surfaces coupled at an inner diameter to one shaft, and friction surfaces coupled at an outer diameter to the other shaft. Further details are provided below.
Turning now to FIGS. 2 and 3, perspective views are shown of an input shaft 58 and an output shaft 60 coupled with respective input clutch plates 62 and 64 and output clutch plates 77, 78 and 80. FIG. 4 is a composite illustration of features depicted in FIGS. 2 and 3. The input shaft 58 is arranged coaxially with the output shaft 60. In the illustrative form the input shaft 58 is smaller in diameter than the output shaft 60 and is thus located radially inward of the output shaft 60. The terms “input” and “output” are not intended to be limiting regarding the use of the shafts. For example, the input shaft 58 can be used to drive the lift fan 54 while the output shaft 60 can be driven by the aircraft engine 50. In these forms the shaft 60 can be used to drive the lift fan 54 and the shaft 58 can be driven by the aircraft engine 50.
In one form the input shaft 58 includes input clutch plates 62 and 64. The input clutch plates 62 and 64 are slidably engaged with the input shaft 58 and are operable to be engaged with corresponding plates associated with the output shaft 60. The input clutch plates 62 and 64 include friction surfaces on one or more of its sides 74 and 76, respectively. The friction surfaces of the sides 74 and/or 76 can be any surface having attributes associated with abradable surfaces or wear surfaces in the brake, clutch, and/or transmission arts such as, but not limited to, toughness, strength, heat resistance, adequate frictional properties, and/or relatively long life. In some forms the friction surfaces can be textured, roughened, and/or grooved. The friction surfaces can be made from a variety of materials including, but not limited to, steel, bronze, iron, iron-bronze, ceramic, metallic ceramic, graphitic carbon and metallic graphite. Though only two input clutch plates 62 and 64 are depicted in the illustrative embodiment, any number of input clutch plates can be used in other embodiments.
The output clutch plates 77, 78, and 80 are operable to be engaged with the input clutch plates 62 and 64. The output clutch plates 77, 78, and 80 include friction surfaces on one or more of its sides 90, 92, and 94, respectively. The outer periphery of the output clutch plates 77, 78, 80 are axially recessed from the friction surfaces on the sides. The friction surfaces of the sides 90, 92, and/or 94 can be any surface having attributes associated with abradable surfaces or wear surfaces in the brake, clutch, and/or transmission arts such as, but not limited to, toughness, strength, heat resistance, adequate frictional properties, and/or relatively long life. In some forms the friction surfaces can be textured, roughened, and/or grooved. The friction surfaces can be made from a variety of materials including, but not limited to, steel, bronze, iron, iron-bronze, ceramic, metallic ceramic, carbon fiber, graphitic carbon and metallic graphite. Though only three output clutch plates 77, 78, and 80 are depicted in the illustrative embodiment, any number of output clutch plates can be used in other embodiments.
The output shaft lug key 88 is coupled to the output shaft 60 through attachment members 96 and 98. The attachment members 96 and 98 can be bolts threadingly received in apertures formed in the output shaft lug key 88, but other forms of attachment members are contemplated herein. To set forth just one non-limiting example, the attachment members 96 and 98 can be fasteners such as rivets.
The output shaft lug key 88 maintains the relative clocked orientation of the output clutch plates 77, 78, and 80 and is received in the illustrative embodiment by a keyway 100 formed by cutouts 101 in the outer periphery of the output clutch plates 77, 78, and 80. In other embodiments the output shaft lug key 88 can be received by apertures formed radially inward of the outer periphery of the output clutch plates 77, 78, and 80. Although one output shaft lug key 88 is depicted, multiple lug keys 88 can be used. The cutouts 101 need not be identical in each of the output clutch plates 77, 78, and 80. In addition, the output shaft lug key 88 need not have the same shape along its length. The output shaft lug key 88 permits the output clutch plates 77 and 78 to slide relative to the output shaft lug key 88.
In a first, uncoupled state (disengaged), the input shaft 58 and the output shaft 60 are not coupled by the clutch 56. The output clutch plates 77, 78, and 80 are in an uncompressed state and do not contact, or partially contact, the input clutch plates 62 and 64. The actuator 104 is withdrawn and the output clutch plates 77, 78 and 80 axially separate naturally due to non-synchronous rotational speeds when left in the uncompressed state. Output clutch plates 77, 78 and 80 separate away from the other plates and out of contact with the input clutch plate 62.
In a second, coupled state (engaged), the actuator 104 provides a force that moves a pressure plate (not shown) axially in the direction of plate 77 and continues moving plate 77 such that it and all clutch plates 77, 78, 80, 62 and 64 are compressed and synchronized. Compression of the output clutch plate 77 with the input clutch plate 62, the output clutch plate 78 with the input clutch plates 62 and 64, and the input clutch plate 64 with the output clutch plate 80 engages the friction surfaces of the sides 74, 76, 90, 92, and 94 to couple rotation of the input shaft 58 with the output shaft 60.
A more detailed discussion of a clutch, clutch plates and their operation may be found in U.S. Pat. No. 8,567,713, the entirety of which is incorporated by reference.
It has been observed that when the lift fan clutch system with interleaved sets of plates is in the disengaged or uncoupled position, the output clutch plates 77, 78, and 80 can, under certain circumstances, tend to flutter, wobble, or have other gyroscopic instability. Such instability may suddenly cause a relatively large increase in drag torque, heat and wear at the keyway 100 which exacerbates the vibration, flutter, wobble or gyroscopic instability. This excessive wear is believed to stem from axial movement, off center plates, tilting plates, and/or interaction between keys and keyways associated with free floating output clutch plates 77, 78 and 80 as described above.
In order to obviate the deleterious effects described above, the disclosed subject matter identifies several types of mitigating systems and methods. A set of solutions are directed to preventing the output clutch plates from falling off center, another set of solutions are directed to maintaining the proper axial position of the output clutch plates during disengagement, others to reducing wear. All the solutions are ultimately directed to preventing an unbalanced condition developing in the output clutch plates and the deleterious resultant vibration, flutter, and wobble.
These and many other objects and advantages of the present subject matter will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.